This invention relates to a method and an apparatus for forming a necked and flanged portion at one end of a bilaterally open cylindrical body, particularly a can body. Such an operation is effected by two inner tools and an outer tool. At least one of the inner tools is rotated by power means. The inner tools are movable axially in the inside of the hollow body relative thereto and subsequently the outer tool is moved radially against the hollow body supported on the inner tools in such a manner that the intended portion of the hollow body is pressed by the outer tool into a concave circumferential contour formed together by the two inner tools. The outer tool and the inner tools are returned into their starting position before deforming a subsequently positioned hollow body.
A conventional apparatus for performing the above-outlined method has two axially movable inner tools for necking and flanging an end region of the cylindrical body. The two inner tools have a contour which corresponds to the intended necked and flanged configuration of the hollow body. At least one of the inner tools is power-driven (rotated). The apparatus further has an outer tool which is movable radially towards the inner tools.
A method and an apparatus of the above-outlined type is disclosed, for example, in published European Application No. 0 290 874. The apparatus disclosed therein is adapted to simultaneously provide necked and flanged portions at both ends of a bilaterally open can body. For each end of the can body the apparatus has a tool assembly, each formed of two inner tools and an outer tool. One of the two inner tools of each tool assembly is a disk affixed to a drivable shaft, while the other of the two inner tools is a swash disk. The fixedly mounted disk has a cylindrical peripheral face adjoined, in the direction of the swash disk, by a tapering contour which corresponds to the necked contour of the finished can body. The diameter of the cylindrical surface is less than the inner diameter of the necked end of the can body and is thus significantly smaller than the inner diameter of the cylindrical wall of the can body. The swash disk, whose radial position is inherently variable and which, accordingly, has no fixed rotary axis, is formed of two annular disks which have the flanged contour of the necked and flanged end of the can body. Both annular disks are radially fixed with respect to one another by an annular shoulder, but are relatively slightly displaceable in the axial direction. The annular shoulder has a diameter which is slightly less than the inner diameter of the non-deformed can body.
It is a disadvantage of the above-outlined conventional apparatus that the can body, because of the diametrical relationships of the inner tools, may be engaged only by a narrow edge of one of the annular disks. Due to this circumstance, a secure entrainment of the can body in the circumferential direction is not ensured and as a result, because of a possible slippage between the can body and the inner tools, the lacquer coating on the can body may be damaged.
Other known devices for neck-forming and flanging the open end of a can body of a two-part can--which in the completed state is formed of two parts, namely, a one-piece bottom-and-can body unit and a lid--essentially comprise a bottom punch which axially immobilizes the can body; two inner tools which, during the neck-forming and flanging phase engage the wall of the can body and an outer tool which effects the neck-forming and the flanging of the can body. Such an apparatus is disclosed, for example, in German Patent No. 2,805,321, to which corresponds U.S. Pat. No. 4,070,888. In the apparatus disclosed therein the two inner tools have different diameters; at least the diameter of one of the two inner tools is substantially less than the inner diameter of the necked can body. The two inner tools are arranged mutually axially displaceably on a common shaft having offset shaft portions. After pulling the can body over the two inner tools by means of the bottom punch, the wall of the can body is pressed against the outer tool by an eccentric feed of the inner tools. While the outer die tool (shaping tool) is axially fixed, the two inner tools are, dependent from the feed depth, axially displaced in mutually opposite directions. Only the outer die tool is driven for rotation; the inner tools thus have to be brought to the desired rpm with the intermediary of the interposed can body. In such a conventional apparatus too, because of the slippage occurring between the can body and the inner tools, lacquer damages on the can body may occur. Further, the ring contour of the outer die tool leads to fold formations in the necked zone of the can body.
In a further known apparatus of the last-described type, the two inner tools also have different diameters and, in such a case too, the diameter of at least one of the two inner tools is substantially smaller than the inner diameter of the necked hollow body forming the rump of a two-part can. Such an apparatus is disclosed in published European Patent Application No. 0 588 048. The inner tools are mounted on a shaft; one of the inner tools is axially displaceable. After inserting the hollow body over the two inner tools and after an eccentric feed of one of the inner tools, the wall of the hollow body is pressed against the inner tools by means of a radial feed of an axially displaceable outer die tool formed of a die roller. The die roller and one of the inner tools are axially displaced as a function of the feed depth. In such a prior art apparatus only the axially displaceable inner tool is driven for rotation. Here too, the lacquer on the hollow body may be damaged and further, a non-uniform flanging may result.
According to yet another conventional apparatus disclosed in European Patent No. 0 520 693, the two axially displaceable and radially fixed inner tools as well as an axially fixed and radially movable outer die tool are provided. Here too, the two inner tools have different diameters and the inner tool with the smaller diameter may rotate in an eccentric position in contact with the hollow body forming the rump of a two-part can. The outer die tool may move radially while the cylindrical hollow body rotates. During this occurrence the outer die tool is pressed into that portion of the hollow body which is to be necked and flanged. This apparatus too, is not capable of producing a uniform flange because of the different diameters of the two inner tools.